1. Technical Field
This disclosure relates to a method for producing a heat-resistant endless belt used as an intermediate transfer belt, a fixing belt, a paper conveying belt, or a paper drying belt which is used for an electrophotographic device such as a copier, a laser beam printer, a facsimile, or an ink jet printer.
2. Description of the Related Art
High pressure affects the paper conveying belt, the intermediate transfer belt, or the like among the heat-resistant endless belts used for the electrophotographic device. Also, high pressure and high temperature affect the fixing belt. Therefore, high heat-resistance and high mechanical strength are required of the heat-resistant endless belts used for the electrophotographic device. For those reasons, a polyimide resin has been used for a material to compose the heat-resistant endless belts. Japanese Patent No. 3411091 discloses a technique to produce a heat-resistant endless belt out of polyimide resin in which a polyimide endless belt is produced by heating polyimide varnish to imidize, after cast-forming polyimide varnish on a surface of an outer circumference of a metallic cylindrical body, for example.
However, there is a problem in Japanese Patent No. 3411091 in that a number of molds are necessary because an imidizing process takes a long time and the cost of molds is high; also, a high initial cost is required because a new mold is necessary every time a size gauge of the mold is changed.
Further, Japanese Patent Application Publication No. Hei11-291348 discloses a technique to produce a polyimide endless belt by processing an inexpensive polyimide sheet, for example.
Japanese Patent Application Publication No. Hei11-291348 shows that the polyimide endless belt is obtained by adhering a non-thermoplastic polyimide film and a thermal plastic polyimide resin together and melt-bonding the thermal plastic polyimide resin.
However, there is a problem in Japanese Patent Application Publication No. Hei11-291348 in that it is difficult to make uniform the layer thicknesses and stiffness between a melt-bonded joint and a non-joint, and also to bond without losing smoothness. As a result, a defective streaky line appears on a fixed image caused by the joint of such a belt, for example.
Furthermore, Japanese Patent Application Publication No. Hei10-000698 discloses a technique to produce a polyimide endless belt by forming groove shaped concavoconvex portions on each of surfaces of end portions of a heat hardening resin sheet or the like and joining the concavoconvex portions fitting each other.
Japanese Patent Application Publication No. Hei10-000698 exemplifies 1) silicon elastic adhesive, 2) urethane elastic adhesive, 3) hot-melt type silicon adhesive, 4) silane-altered polyimide adhesive, and 5) epoxy adhesive as an adhesive applied to the technique, where the adhesive may be used by itself or combined in order to strongly join a polyimide sheet so that the joined sheet can be applied to an intermediate transfer belt.
However, there is a problem in making a fixing belt from the polyimide endless belt in that a silicon elastic layer or a fluorine resin separation layer is formed on the surface of the polyimide endless belt. Here, because the temperature is as high as 300 to 350° C. when forming the fluorine resin separation layer, the adhesive of the joined portion is deteriorated by the heat. Therefore, the adhesive strength is deteriorated.
Here, there is a problem in that an upper temperature limit of a general adhesive of the above described 1) to 3) is 190° C. or less. Therefore, the adhesive strength is deteriorated when the adhesive is heated at 300 to 350° C. to form the fluorine resin separation layer. Another problem is that the adhesive is stiff after being hardened even though the heat-resistance is good; therefore, a defective streaky line appears on a toner-fixed image of a corresponding part of the joined part of the polyimide endless belt.